A copending and commonly assigned U.S. patent application of Robert A. Sprague, which was filed Dec. 4, 1984 under Ser. No. 678,199 on a "Distributed Data Storage Architecture for Block Oriented Solid State Optical Memories" discloses a block oriented solid state optical memory in which the bits of each of the optically addressable data blocks are stored in spatially distributed memory sectors. Another copending and commonly assigned U.S. patent application of Robert A. Sprague and John C. Urbach, which was filed Dec. 4, 1984 under Ser. No. 678,145 on "High Density Block Oriented Solid State Optical Memories", discloses an improved imaging system for optically addressing the data stored in such a memory, thereby increasing its maximum permissible bit storage density. These memories are "block oriented" because the data stored therein is selectively addressable in multi-bit data blocks, and they have "distributed data storage architectures" because the bits of each of the data blocks are stored in spatially distributed memory sectors. Moreover, a copending and commonly assigned U.S. patent application of Robert A. Sprague, which was filed Dec. 14, 1984 under Ser. No. 681,775 on a "Programmable Solid State Optical Memories and Data Writer Therefor" discloses a programmable "read only" memory of the foregoing type, together with a data writer for programming and optically aligning such a memory.
Others have proposed a so-called "concentrated page storage architecture" for block oriented solid state optical memories. According to these proposals, each page or block of data is concentrated within a single, optically addressable memory "sector", so that it can be retrieved on demand by selectively illuminating or "addressing" just that one sector. See, for example, U.S. Pat. No. 3,676,864, which issued July 1, 1972 on an "Optical Memory Apparatus"; U.S. Pat. No. 3,765,749, which issued Oct. 16, 1973 on an "Optical Memory Storage and Retrieval System"; and U.S. Pat. No. 3,899,778, which issued Aug. 12, 1975 on "Means Employing a Multiple Lens Array for Reading From a High Density Optical Memory Storage." However, a distributed data storage architecture is more tolerant of the localized optical defects which are likely to be introduced into solid state optical memories during their fabrication and/or use. It therefore is the preferred architecture, especially for memories having high bit storage densities, such as miniaturized memories and larger, high capacity memories.
Coined descriptors are employed to provide convenient names for the above-described storage architectures. Consequently, it may be helpful to note that the phrases "block of data" and "page of data" are used herein more or less interchangeably. Some of the prior art refers to the storage of optically addressable "pages," so it has been characterized as suggesting a concentrated page storage architecture. Similar terminology could be used to describe the general organization of the data stored in a memory having a distributed data storage architecture, but the preferred terminology provides a more generic description which literally applies to all cases, including one wherein each optically addressable data block comprises a plurality of electrically addressable data segments. As will be appreciated, these data segments might be interpreted as being separate "pages of data" as that phrase is normally used in the data processing field, so alternative terminology has been adopted to avoid confusion.
Block oriented solid state optical memories conventionally comprise a data mask, an array of selectively energizeable photoemitters for optically addressing data stored on the data mask, and an array of photosensors for reading out the optically addressed data. Those that have a distributed data storage architecture additionally include suitable imaging means, such as a shadow mask or a lens array, for imaging the photoemitter array in parallel onto spatially displaced sections of the data mask. Moreover, such a memory is constructed so that the photoemitter array images are optically aligned with respective ones of the photosensors and have sufficient resolution to separately resolve the individual photoemitters. Accordingly, the memory is optically partitioned to define a plurality of spatially distributed memory sectors, each of which is optically subdivided to have a plurality of selectively illuminable memory cells.
To store data in a solid state optical memory having a distributed data storage architecture, multi-bit data blocks are mapped onto its data mask, so that the bits of each data block occupy the memory cells (one bit/cell) which are illuminable or "optically addressable" by a respective one of the photoemitters (one cell/sector). As noted in the aforementioned Sprague application Ser. No. 681,775 filed 12-14-84, the data mask advantageously is an optical recording medium, so that it may be programmed in situ by scanning an intensity modulated write beam across the imaging means at the field angle of successive ones of the photoemitters. That self-aligns the imaging means with the data recorded on the data mask, thereby ensuring that the data can be optically addressed on demand.